1. Field of the Invention
This invention relates to electrophotographic photosensitive materials used in electrophotographic processes. More particularly this invention relates to highly-sensitive photoconductive materials which can be used in any of the existing photographic processes and which has a spectral sensitivity over the entire visible light region.
2. Description of the Prior Art
As electrophotographic photosensitive materials, inorganic photosensitive materials such as amorphous selenium, selenium alloys, cadmium sulfide and zinc oxide and organic photosensitive materials which include, typically polyvinylcarbazole and derivatives thereof, are widely known at present.
Amorphous selenium and selenium alloys have very excellent characteristics as electrophotographic photosensitive materials. They are, however, disadvantageous in that their preparation requires complicated processes for deposition and, further, the thus obtained deposited film is not flexible. Further, photosensitive materials of the dispersion type in which zinc oxide is used have a defect in mechanical strength, so that they are not suited for repeated operations as they are.
Polyvinylcarbazole which is widely known as an organic photoconductive material has excellent flexibility, transparency, film-forming properties, etc., but itself exhibits no sensitivity in the visible region. Various sensitizing methods have, therefore, been devised. However, spectral sensitization of polyvinylcarbazole with a sensitizing dye cannot provide a sensitivity which is sufficient, in practice, for electrophotographic photosensitive materials, although the spectral sensitivity region is extended to longer wavelengths to some extent, and is disadvantageous in that light fatigue is marked. Further, chemical sensitization with an electron-accepting compound can provide satisfactory photographic photosensitive materials only from the standpoint of sensitivity, but problems still remain to be solved with respect to mechanical strength, life, etc.
Organic photosensitive materials of the dispersion type have been actively studied, and many reports have been made thereon. However, photosensitive materials having excellent electrical characteristics and satisfactory sensitivity as an electrophotographic photosensitive material have still not yet been obtained. At the present time, it is reported that phthalocyanine exhibits excellent electrophotographic characteristics when used as a photosensitive material of the dispersion type, but the spectral sensitivity of phthalocyanine lies rather toward longer wavelengths and, therefore, it has the defect of poor red-reproducibility.